Method and apparatus for pressure measurement

ABSTRACT

Methods and apparatus for measuring pressure in a patient are provided which may include any number of features. One feature is a pressure measurement system comprising a pressure source, a compliant bladder, a catheter in communication with the pressure source, pressure sensors, and a controller configured to determine a pressure within the compliant bladder. The pressure measurement system can inflate the compliant bladder with gas or air to determine a pressure within a patient. In one embodiment, the pressure measurement system measures pressure within a peritoneal cavity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/809,043, filed Apr. 1, 2013, which claims the benefit under 35 U.S.C.371 of PCT/US2011/043570, filed Jul. 11, 2011, which claims the benefitunder 35 U.S.C. 119 of U.S. Provisional Patent Application No.61/399,298, filed Jul. 9, 2010, titled “Method and Apparatus forTreatment of a Body Cavity or Lumen and Sensing Foley Catheter”, andU.S. Provisional Patent Application No. 61/393,794, filed. Oct. 15,2010, titled “Hypothermia Catheter and System”. These applications areherein incorporated by reference in their entirety.

INCORPORATION BY REFERENCE

All publications, including patents and patent applications, mentionedin this specification are herein incorporated by reference in theirentirety to the same extent as if each individual publication wasspecifically and individually indicated to be incorporated by reference.

FIELD OF THE INVENTION

The present invention generally relates to measuring pressure within apatient. More specifically, the present invention relates to measuringpressure within cavities and lumens of a patient with an air capsule.

BACKGROUND

Hypothermia has been shown to provide distinct medical benefits tostroke and cardiac arrest patients by limiting the size of theinfarction and related tissue injury if initiated soon enough and if thelevel of cooling is significant enough. Both of these limitations,initiation of and depth of cooling, have made practical application ofthe technology quite challenging particularly in an ambulance or otheremergency settings in the field. Initiation of cooling, for example, isa major issue since most technologies require sophisticated machinerythat would be difficult to place in ambulance so the patient, at best,receives the hypothermic benefit some time after they reach thehospital. Of the technologies that can be initiated in the field,though, such as cooling blankets, cooling caps, etc., the depth ofcooling is a major issue due to surface area limitations, complications(such as intense shivering response) and patient access issues (once theblanket is on, it may be difficult to access the patient).

Infusion of a hypothermic fluid into a patient, such as into a patientcavity such as the peritoneal cavity, adds additional challenges. Theinfusion of a large volume of fluid into the patient cavity can increasepressure inside the cavity. High pressures inside the peritoneal cavitycan cause problems for the patient, putting the patient's health andwell being at risk. Obtaining an accurate measurement of the pressurewithin the patient can be very difficult in hypothermia applications butis necessary to insure the safety of the patient. Access to the cavity,changing volumes of fluid in the cavity, patient movement, and organswithin the cavity all provide challenges for accurate pressuremeasurement within the patient.

Thus, there exists a need for improved devices for rapidly producinghypothermia to treat stroke, severe cardiac events and relatedconditions, particularly in the ability to accurately and easily measurepressure within the patient.

SUMMARY OF THE DISCLOSURE

In one embodiment, a pressure measurement system is provided, comprisinga catheter, a pressure lumen disposed in the catheter and coupled to apressure source, a compliant bladder disposed on the catheter, thecompliant bladder being in communication with the pressure lumen, apressure sensor coupled to the pressure lumen and configured to receivea pressure signal from the compliant bladder via the pressure lumen, anda controller configured to receive the pressure signal from the pressuresensor and to control the pressure source to fill the compliant bladderwith a volume of gas.

In some embodiments, the controller is configured to execute a primingsequence comprising commanding the pressure source to fill the compliantbladder with a first volume of gas, and after filling the compliantbladder with the first volume of gas, commanding the pressure source toremove a second volume of gas from the compliant bladder so thecomplaint bladder becomes partially-filled.

In another embodiment, the controller is configured to execute a primingsequence comprising commanding the pressure source to fill the compliantbladder with gas until the complaint bladder reaches a first pressure,and after reaching the first pressure, commanding the pressure source toremove a first volume of gas from the compliant bladder so the complaintbladder becomes partially-filled.

In an additional embodiment, the controller is configured to execute apriming sequence comprising commanding the pressure source to fill thecompliant bladder with gas until the complaint bladder reaches a firstpressure, and after reaching the first pressure, opening the pressuresource to atmospheric pressure for a first amount of time to remove gasfrom the compliant bladder until the complaint bladder becomespartially-filled.

In some embodiments, the catheter further comprises a fluid infusionlumen and a fluid extraction lumen. In other embodiments, the pressurelumen is disposed in a divider between the fluid infusion lumen and thefluid extraction lumen. In additional embodiments, the pressure lumen isdisposed in an interior wall of the catheter.

In one embodiment, a divider between the fluid infusion lumen and thefluid extraction lumen includes ridges to prevent total obstruction offluid flow in the fluid infusion and extraction lumens during bending orkinking. In another embodiment, the pressure lumen is free floating inthe fluid infusion lumen.

In some embodiments, the system further comprises a second pressurelumen coupled to the pressure source and in communication with thecompliant bladder. In one embodiment, the pressure lumen and the secondpressure lumen are disposed on opposing sides of the catheter.

In some embodiments, the pressure lumen is disposed in an asymmetricwall of the catheter.

In one embodiment, the catheter includes four-extrusions connected endto end, wherein a first extrusion comprises the pressure lumen, andwherein a second, third, and fourth extrusion comprise infusion andextraction lumens. In one embodiment, the infusion lumen occupiesapproximately one-third of a cross-sectional volume of the catheter.

In some embodiments, the controller is configured to periodically repeatthe priming method steps of filling the compliant bladder, then removingair or gas from the bladder until the bladder is partially-filled, toensure accurate pressure measurements.

Another embodiment further comprises at least one displacement balloonin close proximity to the compliant bladder, the at least onedisplacement balloon configured to form a void around the compliantbladder.

A method of measuring pressure in a patient is also provided, comprisinginserting a pressure measurement catheter into a patient, inflating acompliant bladder of the pressure measurement catheter with gas from apressure source coupled to the compliant bladder, after the inflatingstep, removing gas from the compliant bladder so the compliant bladderis partially-inflated, and measuring a pressure of the compliant bladderwith a pressure sensor coupled to the compliant bladder to determine apressure within the patient.

In one embodiment, the removing gas step further comprises removing apredetermined volume of gas from the compliant bladder. In anotherembodiment, the removing gas step further comprises opening thecompliant bladder to a lower pressure for a period of time to remove gasfrom the compliant balloon. In some embodiments, the lower pressure isatmospheric pressure.

In one embodiment, the inflating step comprises inflating the compliantbladder with a first volume of air. In another embodiment, the inflatingstep comprises inflating the compliant bladder to a preset pressure.

In yet another embodiment, the inserting step comprises inserting thepressure measurement catheter into a peritoneal cavity of the patient.In some embodiments, the inserting step comprises inserting the pressuremeasurement catheter into a stomach of the patient. In one embodiment,the inserting step comprises inserting the pressure measurement catheterinto a urinary tract of the patient.

Some embodiments of the method further comprise infusing a fluid intothe patient through an infusion lumen of the pressure measurementcatheter. The method can further comprise extracting fluid from thepatient through an extraction lumen of the pressure measurementcatheter.

In some embodiments, the infusing step comprises infusing a hypothermicfluid into the patient. A method of measuring pressure in a patientreceiving therapeutic hypothermia is provided, comprising, inserting acatheter into a peritoneal cavity of the patient, infusing a hypothermicfluid into the patient to achieve therapeutic hypothermia, and measuringa pressure of the peritoneal cavity with an air-filled pressuremeasurement balloon of the catheter.

A method of measuring pressure in a patient receiving therapeutichypothermia is provided, comprising, inserting a catheter into aperitoneal cavity of the patient, infusing a hypothermic fluid into thepatient to achieve therapeutic hypothermia, and measuring a pressure ofthe peritoneal cavity with an air-filled pressure measurement balloon ofthe catheter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is one embodiment of a pressure measurement system.

FIGS. 2A-2J illustrate various embodiments of a pressure measurementcatheter.

FIG. 3 is another embodiment of a pressure measurement system.

FIG. 4 is one embodiment of a pressure measurement system withdisplacement balloons adjacent to or in close proximity to a measurementballoon.

FIG. 5 is one embodiment of a Foley-style pressure measurement system.

DETAILED DESCRIPTION OF THE DISCLOSURE

Devices and methods for measuring pressure are disclosed. Morespecifically, some embodiments of the present disclosure describedevices and methods for measuring pressure within a patient with acompliant gas-filled bladder or balloon. The compliant gas-filledballoon can be coupled to a gas-filled column located within, forexample, a catheter, to measure the pressure inside of patient cavities,organs, lumens, etc.

The present invention overcomes the limitations of the prior art throughthe use of an air bladder in conjunction with an automated controller toensure that the volume of air required to perform accurate pressuremeasurements is maintained within the air capsule.

FIG. 1 illustrates one embodiment of a pressure measurement system 100,comprising a compliant balloon 102, catheter 104, a pressure line withinthe catheter (not shown), pressure sensors 106, pressure source 108, andcontroller 110. The pressure measurement system 100 can be configured tobe inserted into a patient to measure a pressure within the patient. Insome embodiments, the system is sized and configured to measure pressurewithin patient cavities, organs, or lumens. In one embodiment, thesystem is sized and configured to measure a pressure within theperitoneal cavity of a patient. In another embodiment, the system issized and configured to measure a pressure within the urinary tract ofthe patient, such as within the bladder or urethra. In anotherembodiment, the pressure measurement balloon is inserted into thestomach of the patient.

The compliant balloon 102 may comprise any compliant material. Withinthis disclosure, the compliant balloon may be referred to as a balloon,bladder, membrane, or other similar term. The balloon can comprise anycompliant, flexible, non-porous material configured to expand or retractwith inflation and deflation of a gas or fluid. The balloon 102 maycomprise a thermoset or thermoplastic polymer, silicon, latex, or anyother compliant material used in medical balloon applications, forexample. In some embodiments, “rigid” polymers can be beneficial forpressure measurement applications. In some embodiments, the balloon thatcan be collapsed for insertion and removal. In one embodiment, theballoon may be tacked down by folding and setting of the balloon orthrough application of vacuum to collapse the balloon radially.Alternatively, the tip of the balloon may reversibly engage the tip ofthe catheter and may disengage during air inflation of the capsule.

An important feature is for the balloon to have a sufficient volume fora pressure measurement application. Sufficiency of the volume of theballoon is determined by the ratio of the pressure line volume to theballoon volume. In some embodiments, the volume of the balloon at least15% of the total volume in the pressure lines. In one embodiment, thevolume of the balloon is approximately 8-12 cc and the volume of thepressure lines is approximately 11-16 cc, however larger volumes mayprovide less sensitivity to fill volume.

Referring still to FIG. 1, one or more balloons 102 may be used in thepressure measurement system. In the illustrated embodiment, the balloonis positioned at a distal end of the catheter 104. However, in otherembodiments, the balloon may be located at any location along the lengthof the catheter, so long as it can be positioned within the patient tocollect pressure information. The balloon 102 may be any shape, such asspherical, ribbed, elongated, or with splines. An elongated balloon ispreferred because it can have a large volume but still groom or deflatedown to a small diameter for placement into the patient and removal fromthe patient. In some embodiments, the balloon can have a length ofapproximately 4-8 cm. The balloon may inflate to a diameter ofapproximately 1-3 cm in a pressure measuring configuration, and maydeflate down to a total diameter of approximately 0.1-1 cm in a deliveryconfiguration. It should be noted that, in the delivery configuration,the balloon diameter is limited to the size of the catheter being used.

The balloon may also be asymmetric in a way that it expandspreferentially on the side of the catheter, aligning with holes for aircommunication. This helps ensure that the balloon will not interferewith other functions of the catheter which may occur on the oppositeside of the catheter, such as fluid flow, temperature measurement, oroptical or ultrasound assessment of surrounding tissues.

Catheter 104 can include an independent pressure lumen for communicationbetween the balloon 102 and pressure sensors 106. The pressure lumen isnot illustrated in FIG. 1 as it is disposed within the catheter, butwill be illustrated and described in more detail below. The pressurelumen couples the balloon 102 to pressure sensors 106, providing anair/gas column between the balloon and the sensors. The catheter 104 canfurther include fluid infusion and/or extraction lumens for deliveringfluid to a patient and/or removing fluid from the patient. In someembodiments, the catheter can include separate infusion and extractionlumens. Each of the infusion and extraction lumens may further includeinfusion and extraction ports positioned at specified points along thecatheter, to allow for communication between the infusion/extractionlumens and the outside of the catheter. Further details on a cathetersystem with suitable infusion and extraction lumens and ports aredescribed in U.S. patent application Ser. No. 12/702,165, titled “Methodand Apparatus for Inducing Therapeutic Hypothermia,” filed Feb. 8, 2010.

The catheter may have features to aid in correct depth setting of thepressure sensing balloon including, a retention balloon 105 proximal tothe balloon 104 that can be used as an anchor to the inside of thepatient. In another embodiment, a bend in the catheter proximal to theballoon 104 that can be configured to anchor the catheter inside thecavity. The bend may be flexible enough to pass through an access port(not shown) but offer enough resistance to straightening to allow theuser to feel the bend against the inside of the patient when applying aremoving force to the catheter.

In some embodiments, the connection between the catheter and theremainder of the system is done with a single motion. The user can pushthe catheter into a receiving end until they reach a certain force oruntil there is audible (click) or tactile feedback. Tactile feedback maybe provided by a detent feature, such as a swaged extrusion passing byan O-ring, or by a feature bottoming out into a tapered shaft.

The catheter connection may also complete an electrical circuit or pressa button, allowing the controller 110 to know that the catheter has beenconnected. The connection may have a resistor of a particular value toindicate an identifying piece of information such as lot#, model#, orcalibration. In other embodiments, the catheter may also have an RFIDchip in it to convey information to the controller 110 about informationsuch as lot#, model#, or calibration. In other embodiments, the cathetermay have a fuse or other feature that can be disabled at the end oftreatment for identification of used devices.

FIG. 2A is one embodiment of a cross sectional view of catheter 204,which can be catheter 104 of system 100 in FIG. 1. In FIG. 2A, theinterior of catheter 204 can comprise pressure lumen 212. The pressurelumen may connect to the controller and/or pressure sensors as anindividual connection (e.g., luer connection) or as part of a step thatconnects multiple connections, fluid and/or electrical to the controllerand/or pressure sensors. For applications in which the pressure lumenand balloon are filled with air, the pressure lumen can be as small as0.024″ ID and function as required. FIG. 2B is another embodiment ofcatheter 204 and pressure lumen 212. In FIG. 2B, the pressure lumen doesnot occupy the whole interior of the catheter, but rather, is its ownseparate lumen. The embodiment of FIG. 2B shows the pressure lumen 212being disposed off-center within the catheter. However, in otherembodiments, the pressure lumen can be disposed in the center of thecatheter, or even positioned adjacent to the interior wall of thecatheter. In some embodiments, the pressure lumen may be floating withinan already-existing lumen of the catheter.

In some embodiments, the pressure lumen may be part of a multi-lumenextrusion within the catheter of the pressure measurement system. Asdescribed above, one or more of these lumens may be used for infusion orextraction of fluids to and from a patient. In the embodiment of FIG.2C, catheter 204 can include infusion lumen 214 and extraction lumen216. The pressure lumen 212 can be disposed within either of the lumens.In FIG. 2C, the pressure lumen 212 is shown as a floating lumen withinthe infusion lumen 214. The lumens can be separated by a divider 218, ofany desired thickness. For example, a thicker divider 218 may increasethe cross-sectional strength of the catheter, increasing bend or kinkresistance, at the expense of reducing the total volume of fluid thatcan be infused/extracted by the catheter.

FIG. 2D illustrates an embodiment where the pressure lumen 212 isembedded inside a wall 220 of the catheter. FIG. 2E illustrates anembodiment where the pressure lumen is embedded inside the divider 218of the catheter. In the embodiment of FIG. 2E, positioning the pressurelumen in the center of the catheter allows the catheter to flexsymmetrically during use, and provides for some kink protection becausethe central location of the pressure lumen holds the infusion andextraction lumens at least partially open during flexure.

FIG. 2F illustrates yet another embodiment, wherein the pressure lumen212 is embedded inside of wall 220 of the catheter, and the divider 218includes ridges 222 to prevent total obstruction of flow within theinfusion/extraction lumens during bending or kinking.

In FIG. 2G, the catheter includes two pressure lumens 212 for pressuremeasurement redundancy. Both pressure lumens may be disposed in exteriorwalls of the catheter, as shown. In some embodiments, the pressurelumens can be positioned across from another in the catheter, forexample, spaced 180 degrees apart. This can allow the catheter to benduniformly. In this embodiment, the dual pressure lumens can also serveto prevent total occlusion of the flow path in the infusion orextraction lumens 214 and 216 during bending or kinking. The dualpressure lumens may communicate with the same pressure measurementballoon, or separate balloons located on opposite sides are at differentlocations along the length of the catheter.

In another embodiment, as shown in FIG. 2H, the pressure lumen 212 canbe disposed in an asymmetric wall 224. This design allows for formationof a large extraction lumen 216 (relative to the infusion lumen 214). Insome embodiments, a reinforcing structure, such as a coil or otherdevice, can be used in the extraction lumen or within the walls of thecatheter to aid in preventing kinking.

In FIG. 2I, the catheter 204 can include four extrusions to provide forexcellent kink resistance without needing to add a separatekink-reducing structural component. In this embodiment, the two lowerextrusions can be used as extraction lumens 216, and the upper rightextrusion can be infusion lumen 214. The final extrusion can be used asthe pressure lumen 212. In the illustrated embodiment, the infusionlumen 214 occupies approximately 120 degrees of the catheter, and thepressure lumen occupies approximately 60 degrees of the catheter.

In the embodiment of FIG. 2J, the infusion lumen 214 can be a roundlumen, the extraction lumen 216 can wrap around the infusion lumen, andthe pressure lumen can be disposed in the wall of the catheter 204 nextto the extraction lumen. This embodiment also provides for excellentkink resistance while allowing for efficient fluid infusion and removal.

In some embodiments, the pressure lumen comprises a different materialthan the rest of the catheter. While it is often desirable for thecatheter to be flexible, in some embodiments, the pressure lumen can bemade out of a more rigid material, or the infusion or extraction lumensmay have a braided material in the wall (stainless steel for example) tomake the catheter wall stiffer. This stiffness aids in the prevention ofkinking and isolates the pressure signal from pressure in the otherlumens of the catheter. Depending on the relationship in volume betweenthe pressure lumen and the measurement balloon, this level of isolationmay not be necessary because the lumen wall deflection may createnegligible volume change.

In the embodiments described above, the ratio of cross sectional areabetween the infusion lumen and the extraction lumen can vary from 1:1 to1:2, respectively, but other ratios can also be used. Also, in any ofthe embodiments described above, the catheter or even the individuallumens can include anti-kinking devices, including but not limited to astructure within one or more of the catheter lumens or walls such as acoil, a braid, or an extrusion in a V, Y, or + shape.

In some embodiments, the catheter can be designed in a way that enablesit to groom down in the region of the balloon to a smaller diameter toallow for fitment of an access port over the catheter. In oneembodiment, the catheter grooms down to fit through a 5 mm access port.In one embodiment, the catheter necks down to a smaller outer diameterdistal to the end of the infusion lumen. The balloon can then residedistal to the termination of the infusion lumen. In some embodiments,the catheter may have three lumens on the proximal end (e.g., infusion,extraction, and pressure), but reduce the number of lumens along itslength. For example, after the infusion holes, the infusion lumen couldend. After the pressure lumens/balloon, the pressure lumen could end.This can be accomplished with stop-lumen extrusion technology, by reflowof extrusion material, or by butt-joining different extrusion designs toeach other.

Referring back to FIG. 1, the system 100 can further include one or morepressure sensors 106. The pressure sensor(s) 106 can be any type ofpressure sensor configured to measure air or fluid pressure, as known inthe art. In some embodiments, a pressure sensor is included insidecontroller 110, however they are described and illustrated separately inthis disclosure to ease in the description. The pressure sensors may bereusable or disposable. In one embodiment, the sensors are a reusablecomponent in the controller. The advantage of using pressure sensorscoupled to the pressure lumen and balloon with air is that the sensorscan be at a different elevation than the balloon without having anoffset in the pressure signal, owing to the negligible density of air.During a medical procedure in which a catheter is inserted into apatient and the balloon is not visible, more accurate pressuremeasurements can be made without having to worry about aligning theelevation of external pressure sensors with a (sometimes unknown)balloon depth.

Temperature compensation to account for differences in temperaturebetween the pressure sensor location and the balloon location has notbeen found to be necessary in the pressures and temperatures fortherapeutic hypothermia with peritoneal lavage. However in someembodiments, for added accuracy, temperature can be measured in thecatheter in the vicinity of the balloon with a temperature sensor(thermistor, thermocouple, optical sensor, etc.).

Referring still to FIG. 1, the system 100 can also include a pressuresource 108 to provide gas or air pressure to the pressure lumen andballoon. In some embodiments, the pressure source is a manual pressuresource, such as a syringe or bellows. In other embodiments, the pressuresource is automated, such as a pump. Any kind of automated pump can beused to move gas, air, or fluid into the pressure lumen and balloon,such as a diaphragm, syringe, gear, bellows, peristaltic pump, etc. Inother embodiments, a compressed air supply, such as in a hospital, canbe used to fill the pressure lumen and balloon with air.

When air is the material used to fill the balloon, the design may havegreat sensitivity to the presence of fluid contaminants in the pressuremeasurement lumen. With small diameter pressure lumens, the surfacetension of fluid can prevent small volumes of fluid from moving withinthe lumen thereby damping, diminishing, or even eliminating a pressuresignal from reaching the external sensors. Thus, various embodiments canmitigate against fluid blockage of the pressure lumen. In oneembodiment, the pressure lumen can be lined with a hydrophobic materialthat will reduce the attraction between an undesired fluid and thepressure lumen wall. In another embodiment, the addition of a surfactantor similar chemical can reduce the surface tension of the fluid in thepressure lumen. In another embodiment, a hydrophilic fiber can bedisposed within the pressure lumen. The hydrophilic fiber can have asmaller diameter than that of the pressure lumen, so gas or air canstill travel along the pressure lumen. Fluid will be attracted to thefiber and be less likely to wet the walls of the pressure lumen, therebyleaving space for the pressure signal to travel. In one embodiment, ifthe hydrophilic fiber becomes saturated with fluid, the system caninclude an indicator or a circuit coupled to the control system to alertthat the fiber is full. For example, a saturated fiber could close acircuit to set off an alarm in the control system, or alternatively, thefiber could change color when saturated and be checked occasionally by amedical worker (e.g., a nurse). In another embodiment, the pressurelumen can include a combination of a wick and hydrophobic coating on theinner wall of the lumen.

In yet another embodiment, the pressure lumen may be hydrophobic andhave an irregular cross-section involving one or more projections in oneor more directions. This irregular lumen will be resistant toobstruction by water droplets which will want to form spherical bodiesbased on the properties of the surface tension of water in the presenceof a hydrophobic material. With droplets forming in the center of thelumen, said projections will resist obstruction and provide a continuousair channel from proximal end to the distal end of the catheter.Obstruction by a fluid formation in the catheter may also be preventedby the use of intermittent evacuation of the balloon and pressure lumen.This method may be used on its own or in conjunction with any of theother embodiments outlined above and entails intermittently evacuationthe balloon and the pressure lumen to remove fluid excess into aproximal fluid collection reservoir or water scavenger. In combinationwith the automated balloon priming to appropriately refill the balloon,this feature will allow for intermittent removal of accumulated waterwhich, if not removed, could potentially overwhelm the lumen.

Additional solutions to this issue of fluid in the pressure lumen aredisclosed. In one embodiment, a pump can move air through the pressurelumen at all times that the catheter is disconnected to keep thepressure lumen free of fluid. In another embodiment, the catheterincludes separate pressure lumen and infusion lumen connectors, ratherthan a single connection that connects to the rest of the system with asingle motion. In another embodiment, the pressure lumen can have asleeve, sheath, cap, or other protective mechanism over the proximal endof the pressure lumen that is configured to slide out of the way uponconnection to the rest of the system. In one embodiment, a cap can bespring loaded so as to engage whenever the pressure lumen isdisconnected from the system. In another embodiment, a stylet can beplaced in the pressure lumen of the catheter and be removed just priorto connection with the system.

In FIG. 1, the system further includes a controller 110. In manyembodiments, the controller can be configured to automatically controlone or more parameters related to pressure measurement, calibration, andinfusion or extraction of fluid to and from a patient. It should beappreciated that controller 110 can also be configured to perform avariety of operations including communicating with external devicesincluding devices linked over the Internet; wireless peripheral devices;data operations; and various power management functions.

Controller 110 can include one or both of analog or digital circuitryfor performing its control operations. The controller will alsotypically be configured to receive one or more inputs, such as frompressure sensors 106. Typically, the controller will include a computerprocessor which is configured to execute one or more electronicinstruction sets contained within a software module, which can be storedin memory onboard the controller. Additionally, controller 110 can beconfigured to be programmed by the user (e.g., using a user interface orby an external device such as a wireless device) to allow for manualcontrol of one or more operations of the system (e.g., infusion rate,extraction rate, pressure line calibration, etc).

Methods of measuring pressure with the systems described herein will nowbe described, with reference to FIGS. 1 and 3. The pressure measurementsystem of FIG. 1, particularly balloon 102, catheter 104, pressuresensors 106, pressure source 108, and controller 110, can correspond toballoon 302, catheter 304, pressure sensors 306, pressure source 308,and controller 310 of FIG. 3. In one embodiment, pressure sensors 306can be zeroed to atmospheric pressure while the system is in a standbymode, before use. Next, the catheter 304 can be placed into a spacewithin the patient P for which a pressure measurement is desired withthe aid of an access device. After removal of the access device, thecatheter can be connected to the controller 310 and/or pressure sensors306. In some embodiments, as described above, the controller isconfigured to automatically detect when the catheter is connected to thecontroller.

In one embodiment, upon connection of the catheter, the controller canclose a first valve 326 disposed between the pressure source 308 (e.g.,a pump) and the catheter 304, isolating the pressure source 308 from thecatheter 304. In one optional embodiment, the system can evacuate theballoon and pressure lumen prior to closing the first valve. Thecontroller can then open a second valve 328 disposed between thepressure source and the outside to open the pressure source up toatmosphere and enable the pressure source to fill with atmospheric air.Once the pressure source is filled with air, the first valve can open toconnect the pressure source and catheter again.

Next, the pressure source can fill the pressure lumen of the catheterand balloon 302 with air/gas. In some embodiments, the controller 310fills the balloon 302 until the balloon reaches a specified pressure orvolume (based on the volume of the balloon). In some embodiments, whenthe specified pressure or volume is reached it serves as an indicator tothe controller that the balloon is properly coupled to the controllerand rest of the system. In some embodiments, the specified pressure ofvolume is the pressure or volume to fully fill the balloon with air/gas.Thus, in one embodiment, the pressure source fills the pressure lumenand balloon with air or gas until the balloon is fully inflated.

In one embodiment, the controller can pause for a set period of time andperform a leak test to evaluate the system for leaks in the balloon orcatheter connections. The leak test can ensure that the balloon isviable and ready for use in pressure measurement. The leak test candetermine that the balloon is leak free based on expected pressureand/or volume characteristics.

Next, in one embodiment, the controller can remove a predeterminedamount of air or gas from the balloon 302 to make the balloonpartially-filled. The amount of gas/air removed from the balloon can bepressure-controlled or volume-controlled. In one embodiment, a bellowspump displaces a fixed amount to remove a fixed volume of air from theballoon. Additionally, the removal of air or gas from the balloon can betime based, for example the balloon could be vented to atmosphericpressure for a specified amount of time (e.g., for fractions of secondsto seconds). Finally, once the proper amount of gas or air is in theballoon and pressure lumen, the first valve 326 between the pressuresource 308 and the catheter 304 can be closed, rendering the system 300ready for pressure measurement. Even with bellows/syringe type pumps,closing the first valve is beneficial because it decreases the airvolume of the sensing system, making the pressure in the system moresensitive to changes in the catheter balloon.

During use, the controller 310 may periodically evaluate the balloon 302and the catheter connections by refilling the balloon to a set pressure.Additionally, the controller can perform a leak test prior to using thesystem for a pressure measurement by observing the air pressure signalfor drift. Retesting the system is very useful in long procedures, wherethere is potential for manipulation and/or damage to the catheterbetween pressure measurements.

In some embodiments, the controller can automatically maintain a desiredpressure or volume in the balloon 302. As with any air or gas filledballoon, air loss or pressure loss can always be a problem. However,this air or pressure loss is unpredictable and can vary based on theenvironment and type of procedure in which the balloon is used. Thepresent system can overcome this limitation by intermittently fillingthe balloon 302 to a desired pressure or volume of gas/air. In someembodiments, after filling to the desired volume or pressure, thecontroller can automatically remove a specified amount of gas or airfrom the balloon to make the balloon partially-filled or more compliant.In another embodiment, the controller can completely evacuate theballoon at specified intervals during a procedure, then fill the balloonto the optimal pressure or volume or the leak test pressure or volume inthe manner described above.

The controller may also test the connection between the balloon and thepressure sensor by analyzing the pressure signal for the pressure cyclesassociated with patient respirations. If the balloon was not inflated orwas over-inflated, these respirations would not be evident. Respirationand patient activity can create variations in pressure with magnitudesup to 100 mm Hg (coughs). Air pressure signals occur when the balloonhas a nominal amount of air in it and that volume can compress andexpand in response to changes in surrounding pressure. If a balloon isunder-inflated, the baseline pressure of the cavity may be sufficient tocollapse the volume of air in the balloon, eliminating the air/gaspressure signal since no further compression of the air/gas can takeplace. A similar problem occurs if the catheter balloon is overinflated. Cavity pressures and fluctuations below the catheter balloonpressure will not affect the pressure in the balloon and thus goun-measured. For example, if the catheter balloon was inflated to 200mmHg, the 100 mm Hg pressure from a cough would not compress thecatheter balloon and generate a pressure signal.

The system may have an expected range of volumes of air that arerequired to fill the balloon. This information can be used to detectwhether or not there is a kink in the line between the sensors and theballoon. For example, if pressure readings from the pressure sensorsindicate that the pressure in the balloon is at the expected value, buta lower volume of air or gas was filled in the balloon to attain thatvalue, then the controller can determine that there is a kink in thepressure lumen.

Referring again to FIG. 1, FIGS. 2A-2J, and FIG. 3, in one embodimentthe catheter of the present disclosure may be used in methods to measurepressure in a patient while inducing and maintaining therapeutichypothermia in the patient. While this disclosure is directed to thepressure measurement aspect of the procedure, further details anddescription regarding the therapeutic hypothermia aspect of theprocedure may be found in the U.S. patent application Ser. No.12/702,165 referenced above.

In a first step of the method, the catheter is inserted into aperitoneal cavity of a patient. Next, the cavity pressure measurementcatheter is connected to the controller 108, primed, and made ready tomeasure pressure in the manner described above. Specifically, thepressure source can fully inflate the balloon with air or gas, thenremove a predetermined volume of fluid from the balloon until it ispartially-inflated. An initial pressure reading can be taken with theballoon 102 of system 100.

Next, controller 110 can initiate infusion of a hypothermic fluid intothe peritoneal cavity to induce therapeutic hypothermia in the patient.As the fluid is being infused into the patient, the pressure sensors canacquire pressure signals from the pressure lumen and balloon 102indicating a pressure within the peritoneal cavity. In some embodiments,the pressure measurements are taken in real time. In other embodiments,the pressure measurements are taken at pre-determined intervals.

In another embodiment of the pressure measurement system, referring toFIG. 4, the system can include a mechanism for protecting the pressuremeasuring balloon from interference by foreign objects touching theballoon. In FIG. 4, catheter 404 of system 400 can further includedisplacement balloons 430 adjacent to or in close proximity to pressuremeasurement balloon 402. After insertion of the catheter into a patientcavity or lumen, displacement balloons 430 can be inflated to form avoid 432 around the pressure measurement balloon 402. The balloon canthen be primed and readied for pressure measurement following the stepslisted above. The displacement balloons form a void around the pressuremeasurement balloon to protect the balloon from touching foreignobjects, such as organs within a dry patient cavity. One benefit of thedisplacement balloons is that they can be deflated to a small diameterduring insertion of the patient so as to be constrained through theaccess device.

Referring now to FIG. 5, in another embodiment, a pressure measurementsystem 500 can incorporate a modified Foley catheter speciallyconfigured to measure pressure and other parameters in the urinarytract, such as within the urethra and/or bladder. As such, the catheter504 of FIG. 5 can be sized and configured to be inserted into theurinary tract of a patient. In FIG. 5, the catheter 504 can include aballoon 502 coupled to a pressure lumen, as described above.Additionally, the catheter can include a retention balloon 505configured to hold the catheter in place. In some embodiments, thecatheter includes sensors 534 disposed between the pressure balloon andthe retention balloon, the sensors configured to measure pH, nitrate,oxygen, hemoglobin, and/or temperature.

In alternative embodiments, other portions of the Foley catheter may beconfigured to sense one or more of the following parameters with sensors536 and 538: urine pH, urine oxygen content, urine nitrate content,respiratory rate, heart rate, perfusion pressure of bladder wall and/orurethra, temperature inside bladder and/or urethra, electrocardiographyvia sensors on the bladder wall and/or urethra, respiratory volume,respiratory pressure, peritoneal pressure, urine glucose, blood glucosevia urethral mucosa and/or bladder mucosa, urine proteins, urinehemoglobin, blood pressure, and any other physiologic parameter that canbe measure in urine or from the urethra and/or bladder wall.

In one embodiment, the catheter can sense a minimum of two parameters,but may be limited to a single parameter for focused applications (i.e.,respiratory rate in a patient in respiratory distress). The respiratoryrate, relative tidal volume, peritoneal pressure, heart rate and/orrelative cardiac output may be measured simultaneously, as well, byconnecting a balloon with a flaccid wall or semi-tense wall to anexternal pressure sensor via a lumen that may be filled with liquidand/or gas. These parameters may also be measured, alone or in concertwith other parameters, through the use of pressure measurementmodalities other than the external pressure sensor. These may include: adeflecting membrane inside of the catheter, MEMs technology, acatheter-based sensor and/or other embodiments.

In some embodiments, as well, the catheter may include a blood pressuresensing element which may take many forms, one of which involves aninflatable member (either a separate balloon or, ideally, a balloon influid communication with the retention and/or pressure sensing balloon)which may be optically analyzed as it is inflated to determine at whichpressure the vessels within the urethra are blanched and blood flow isstopped. This will provide a highly accurate reading of the perfusionpressure of the urethra which provides an indication of both overallblood pressure and vascular resistance. This implantable perfusionpressure device may be used to provide early detection and/or monitoringof a variety of disease conditions including sepsis, shock, hemorrhage,etc. and can usually detect these conditions in the early stages. Thismethodology may also be used to detect perfusion pressure in other areasof the body with an intermittently inflatable member and opticaldetection of blood flow and/or presence of blood.

Other modalities may be used to detect that the tissue has beenblanched, as well, with the critical component being that of theintermittent inflation within the lumen, body cavity or bodily tissuesto provide the compression of the vasculature. Relative cardiac outputand relative tidal volume may be calculated, as well, based on thedeflection of the pressure sensor and/or other force gauge. If sampledfrequently enough (i.e., 2 Hz or faster), the respiratory excursion cannot only be counted, but they can be quantified in a relative manner tothe amplitude of the excursions at the time of catheter placement.Larger excursions mean either heavier breathing or, in the setting of anupward drift in the baseline, a higher peritoneal pressure. The smallpeaks on the oscillating respiratory wave, caused by the pumping heart,may be tracked as well, and the amplitude of this wave may be used, inthe setting of a relatively constant peritoneal pressure, to determinethe relative cardiac output.

As for additional details pertinent to the present invention, materialsand manufacturing techniques may be employed as within the level ofthose with skill in the relevant art. The same may hold true withrespect to method-based aspects of the invention in terms of additionalacts commonly or logically employed. Also, it is contemplated that anyoptional feature of the inventive variations described may be set forthand claimed independently, or in combination with any one or more of thefeatures described herein. Likewise, reference to a singular item,includes the possibility that there are plural of the same itemspresent. More specifically, as used herein and in the appended claims,the singular forms “a,” “and,” “said,” and “the” include pluralreferents unless the context clearly dictates otherwise. It is furthernoted that the claims may be drafted to exclude any optional element. Assuch, this statement is intended to serve as antecedent basis for use ofsuch exclusive terminology as “solely,” “only” and the like inconnection with the recitation of claim elements, or use of a “negative”limitation. Unless defined otherwise herein, all technical andscientific terms used herein have the same meaning as commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs. The breadth of the present invention is not to be limited bythe subject specification, but rather only by the plain meaning of theclaim terms employed.

We claim:
 1. A method of measuring pressure in a patient, comprising:anchoring a pressure measurement catheter within a patient via aretention balloon; inflating a pressure sensing membrane disposed on thepressure measurement catheter; measuring a pressure of the pressuresensing membrane with a pressure sensor in communication with thepressure sensing membrane and with a controller to determine a pressurewithin the patient; and controlling a flow of fluid to the pressuresensing membrane via the controller.
 2. The method of claim 1 furthercomprising removing a volume of gas from the pressure sensing membrane.3. The method of claim 2 wherein the removing a volume of gas stepfurther comprises opening the pressure sensing membrane to a lowerpressure for a period of time to remove the gas from the pressuresensing membrane.
 4. The method of claim 3 wherein the lower pressure isatmospheric pressure.
 5. The method of claim 1 wherein inflating furthercomprises inflating the pressure sensing membrane with a first volume ofair.
 6. The method of claim 1 wherein inflating further comprisesinflating the pressure sensing membrane to a preset pressure.
 7. Themethod of claim 1 wherein inflating further comprises inserting thepressure measurement catheter into a peritoneal cavity of the patient.8. The method of claim 1 wherein inflating further comprises insertingthe pressure measurement catheter into a stomach of the patient.
 9. Themethod of claim 1 wherein inflating further comprises inserting thepressure measurement catheter into a urinary tract of the patient. 10.The method of claim 1 further comprising infusing a fluid into thepatient through an infusion lumen of the pressure measurement catheter.11. The method of claim 10 further comprising extracting fluid from thepatient through an extraction lumen of the pressure measurementcatheter.
 12. The method of claim 10 wherein the infusing step comprisesinfusing a hypothermic fluid into the patient.
 13. A pressuremeasurement system, comprising: a catheter having a pressure lumendisposed in the catheter; a pressure sensing membrane disposed on thecatheter, the pressure sensing membrane being in communication with thepressure lumen; a retention balloon configured to anchor the catheterwithin a patient body; a pressure sensor coupled to the pressure lumenand configured to receive a pressure signal from the pressure sensingmembrane via the pressure lumen; and a controller configured to receivethe pressure signal from the pressure sensor and to control a flow offluid to the pressure sensing membrane.
 14. The system of claim 13further comprising a pressure source coupled to the pressure lumen. 15.The system of claim 14 wherein the controller is configured to controlthe pressure source to control the flow of fluid from the pressuresensing membrane.
 16. The system of claim 13 wherein the pressuresensing membrane comprises a pressure sensing balloon.
 17. The system ofclaim 14 wherein the controller is programmed with instructions toexecute a priming sequence, the instructions comprising: commanding thepressure source to fill the pressure sensing membrane with a firstvolume of fluid; and after filling the pressure sensing membrane withthe first volume of fluid, commanding the pressure source to remove asecond volume of fluid from the pressure sensing membrane.
 18. Thesystem of claim 17 wherein the instructions further compriseperiodically repeating the priming sequence ensure accurate pressuremeasurements.
 19. The system of claim 14 wherein the controller isprogrammed with instructions to execute a priming sequence, theinstructions comprising: commanding the pressure source to fill thepressure sensing membrane with the fluid until the pressure sensingmembrane reaches a first pressure; and after reaching the firstpressure, commanding the pressure source to remove a first volume offluid from the pressure sensing membrane.
 20. The system of claim 19wherein the instructions further comprise periodically repeating thepriming sequence to ensure accurate pressure measurements.
 21. Thesystem of claim 14 wherein the controller is programmed withinstructions to execute a priming sequence, the instructions comprising:commanding the pressure source to fill the pressure sensing membranewith the fluid until the pressure sensing membrane reaches a firstpressure; and after reaching the first pressure, opening the pressuresource to atmospheric pressure for a first amount of time to remove thefluid from the pressure sensing membrane.
 22. The system of claim 21wherein the instructions further comprise periodically repeating thepriming sequence to ensure accurate pressure measurements.
 23. Thesystem of claim 14 wherein the controller is programmed withinstructions to execute a priming sequence, the instructions comprising:commanding the pressure source to remove the fluid from the pressuresensing membrane for a set period of time.
 24. The system of claim 23wherein the instructions further comprise periodically repeating thepriming sequence to ensure accurate pressure measurements.
 25. Thesystem of claim 13 wherein the controller is programmed withinstructions to execute a leak test sequence, the instructionscomprising identifying drift in the pressure signal.
 26. The system ofclaim 13 wherein the catheter further comprises a fluid extractionlumen.
 27. The system of claim 13 wherein the catheter includes atemperature sensor.
 28. The system of claim 13 wherein the catheter is aFoley type catheter.
 29. The system of claim 13 wherein the controlleris further configured to automatically detect when the catheter isconnected to the controller.
 30. The system of claim 13 wherein thecontroller is configured to collect identifying information from thecatheter.
 31. The system of claim 30 wherein the controller isconfigured to detect when a predetermined pressure or volume is reachedby the compliant bladder as an indication of the catheter being properlyconnected to the controller.